Hmm, we build pre-compiled modules (although on Windows) for every supported version of PHP, and we didn't observe this behavior. The person who created the PHP generator will be available only in a week, and he'll be able to try to reproduce the issue on his side, and make the changes if necessary.

On a side note you have quoted Zend API version number, which implies that Zend is present on your system. And also zend files are referenced and accessed by the compiler.

I have downloaded (updated) PHP 5.6 into Ubuntu 15.10 . Then I've successfully built the extension with PHP 5.6.

I can imagine that PHP developers have introduced some breaking change (unintentionally of course) into version 5.5, and, as this is not the latest version (and even not the second latest), there was not enough testing to detect this change and find it breaking.

Unfortunately in this situation there's not much one could do besides upgrading to something more recent. Note, that PHP 7 is probably not a good candidate for a working site due to the number of breaking changes in it. SecureBlackbox 15 will support PHP 7 in the upcoming build or in the build next to the upcoming.